Miso Soup May Fight Breast Cancer

June 17, 2003 -- The "miso" in Japanese miso soup is a paste made from fermented soybeans -- and it may be a powerful weapon against breast cancer.

Researchers have long pointed to soy products as possibly having a protective effect since women in Japan and other Asian cultures have much lower breast cancer rates than American women.

Soy is an important part of the Asian diet. Isoflavones -- naturally occurring chemicals found in abundance in soy products -- are believed to block the growth of certain tumors.

To further investigate this connection, a group of Japanese researchers has conducted possibly the largest study thus far of soy, isoflavones, and breast cancer.

The study -- led by Seiichiro Yamamoto, PhD, an epidemiologist with the National Cancer Center Research Institute in Tokyo, Japan, appears in this week's issue of the Journal of the National Cancer Institute.

The Evidence

In it, Yamamoto and colleagues identified 21,852 women between the ages of 40 and 59 and surveyed them about various lifestyle issues, including their diet.

They traced the women 10 years later and found that 179 had been diagnosed with breast cancer. Again, they surveyed all the women about their diet -- how frequently they ate miso soup and soy foods such as soybeans and tofu. The researchers then calculated the amount of isoflavones consumed.

Researchers found that:

75% of the women consumed miso soup almost daily; of those, 23% had one cup per day, 43% had two, and 34% had three or more per day.

45% had soy foods almost daily, 35% ate soy foods three or four times a week, 17% had it one or two times a week, 2% almost never ate soy foods.

Women with the most isoflavones in their diet had the lowest risk of breast cancer. This was especially true of postmenopausal women.

Eating soy foods in general, however, did not lower the risk of breast cancer.